text:
Are helicopters reinforced asymmetrically?
Helicopters are under a constant torque due to the action-and-reaction forces caused by the rotation of the rotor(s). In the tail rotor and tandem rotors configuration, the airframe is experiencing tension on one side and compression on the other. A weak airframe would be twisted by the strong torque produced by the rotors.
Are opposite sides of a helicopter airframe reinforced differently do due with the difference in stress?

This is an unusual, yet very interesting question!

Looking at the pictures of a Bell 47 I can't see any asymmetric structure.

@TomMcW Ah, hmmm.  I'll delete, fix and re-add.  Thanks.

I can only speak directly on 6 models. R22, B206, Westland Wessex, Puma, Chinook and Schwiezer 269. All of those are strengthened with the normal stringers, ribs and panels on both sides. The power output of a typical tail rotor is in the order of 50-100 hp. This doesn't need special strengthening but this is probably a good enough sample of different types to conclude that most, if not all, do not use special strengthening to counter torque.

As far as i know, the helicopter airframes are not reinforced asymmetrically due to this reason. Note that the helicopter has to yaw in both ways- so there is no point in reinforcing only one side.
The helicopter airframes are not weak- they are designed to withstand the full envelope of expected loads. Also, it is easier to design and manufacture a symmetric helicopter structure.
That said, I've personally seen at least one case where the torque has affected one side of the helicopter more than the other locally (especially in tail fin area), though the effects were not considered serious enough to warrant a design change.

But isn't that yawing is accomplished by reducing or increasing slightly the tail-rotor torque that  balances the main-rotor torque?

@DJohnM In a hover, the forces are in balance.  You can push a hovering helicopter around with your hands.

In balance, so the copter isn't turning, but the two forces are trying to bend it?

@DJohnM My point is that we are not talking about massive forces trying to tear the machine apart.  A typical light helicopter, with the weakest fuselage, is expending perhaps 10-15hp from the tail rotor at the end of a long arm.  Asymmetric strengthening is simply not required.


text:
Is « Shepherd One » really used internationally by air traffic control for Pope's flight?
CNN:

The President flies on Air Force One. The Pope flies on "Shepherd
  One." That's the Federal Aviation-approved call sign for the Boeing
  777 in which he'll be traveling around the United States, according to
  an official from American Airlines, which will be operating the plane.

Wikimedia:

Shepherd One is the international call sign of any aircraft carrying
  the pope onboard. The airline which is used for such transportation is
  usually Alitalia

Source
Perdue site ('Cradle of Astronauts'):

Flying Pope Francis – Purdue alum honored to fly 'Shepherd One'

From Crux Now catholic press:

The plane isn’t really called “Shepherd One.” People in the United States
  call it that, but the phrase is a media conceit rather than an
  actual call sign.

Ghafla.com:

Did you know it’s Americans who baptized the plane carrying the Pope
  ‘Shepherd One’? Well, their very own presidential jet is called ‘Air
  Force One’ so they thought since the Pope is a shepherd leading the
  Catholic Church, his plane should be called ‘Shepherd One’.

Question: Does ATC around the world, starting with Italy and the US, uses the specific call sign Shepherd One?

The FAA declared that as an official call sign for 2015-09-21 to 2015-10-15.

The order it cancels (.pdf here) had the bottom row filled out wrong (SHEPRD1 and "SHEPHERD ONE" were transposed, and "SHEPHERD" was typoed).
A document released on 2016-05-26 lists it in the "deleted special assignment" table (here).

So it's not a permanent reserved identifier in the US; but it might be recurring.
Wikipedia claims here (and here) that in Italy the Papal flights are named "Volo Papale ###", where the ### is a serial number (seemingly the number of times this Pope has flown).  I'll admit that I haven't been able to find anything akin to faa.gov for Italy, France, Australia, or the UK which would corroborate either "Volo Papale" or "Shepherd One".

Typically, the Pope flies on a chartered Alitalia Jet. The Pope's flight is often nicknamed "Shepherd One" by the press, while the actual callsign is "Volo Papale" (papal flight, in Italian) followed by a serial number.

Thanks, what about other countries, specially Italy?

@mins I couldn't find anything solid, but it appears "Volo Papale ###" is what gets used in Italy.  Shepherd One seems to be created by the media and the FAA plays along.  (Updated answer)

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text:
Why don't we have yokes that look like steering wheels?
This question came across my mind when I was thinking about cockpit design vs car design: why don't we have yokes that look like steering wheels?
The first advantage I can think of is more gestures to hold the yoke. You can hold a steering wheel in many ways, e.g. 2 & 10 o'clock, 3 & 9 o'clock, top, bottom, one hand, both hands etc. And one can still pull or push the yoke even if it's circular.
Secondly, in most (if not all) of the yokes, full aileron deflection is achieved when the yoke is rotated approximately 90 degrees. Would it be beneficial if it's 180 degree instead, allowing more fine control?

As far as I can remember, the only times I use anything like full aileron deflection is when landing or taxiing in a crosswind.  Otherwise, control movements are fairly small, probably no more than the arc of the yoke, and done with fingertip pressure.

Another good question would be: why do we use steering wheel instead of yokes on cars?

Short answer: Because you only use one hand on the yoke.
Longer answer: In an airplane, you almost always fly with only one hand on the yoke (or none, as the case may be.) You will be using your other hand for power adjustments, setting flaps, adjusting radios, setting instruments, writing, etc.
In a car, power is adjusted with your feet, so you don't need your second hand for power adjustments and there aren't really any other particularly critical controls that need to be manipulated frequently or precisely. However, in an airplane, you have to be able to precisely control three axes of rotation, not just one like in a car. As such, your feet are needed for yaw control (and differential braking,) which means power must instead be controlled by hand. So, there's no need for the various grip positions that you could use with a wheel because you don't want your second hand on the yoke in the first place.
Additionally, having a 90-degree angle (or nearly so, as the case may be) allows for a better grip than the smooth curve of a steering wheel. You can place 2 or 3 fingers above the horizontal bar and the others below, which prevents your hand from slipping up or down the control wheel, as is possible with a normal car steering wheel.
As far as the second question of whether it would be better to have 180 degrees equal full deflection, that would mean you would either need 2 hands on the yoke in order to command full deflection, which is not good for the reasons already mentioned, or have a weaker grip on the yoke that would allow you to rotate it 180 degrees either direction. If you have a firm grip on the yoke, your wrist will simply not be able to rotate enough to turn it upside down without releasing your grip.
It's also important to note the difference here between what the yoke controls versus what a car steering wheel controls. A car steering wheel directly controls your turn rate. Thus, a car whose steering wheel is in the neutral position will not be turning. In an airplane, however, your current bank angle controls your turn rate. An aileron deflection changes your bank angle. Having the ailerons in the neutral position will not cause you to fly straight forwards, but rather will simply leave your bank angle (and thus your turn rate) at its present value (if we ignore the effects of dihedral and such.) Thus, you don't need as much possible input control range to get precise turn rate control.

"In a car, (…) there aren't really any other particularly critical controls that need to be manipulated frequently or precisely" - gearbox? ;)

@el.pescado: Exactly, at least for those of us who choose to drive cars without assistive technology for the handicapped - AKA automatic transmission.  And in my hybrid, I've installed a setup which allows me to use one hand to control the electric assist separately from the accelerator pedal.

@el.pescado A gearshift is a discreet control. It doesn't require a great deal of precision. And if you need to shift frequently during sharp turns you're probably doing it wrong.

@reirab, modern gear boxes don't require precision but older gear boxes that predate syncros or even helical cut gears require a great deal attention to shift if you intended to make them last. Not to mention any kind of heal toe (or other double clutch) down (or up) shifting that may require you to keep your hand on the shifter for an extended time.

@reirab, I dare you to tell any racing driver that shifting while turning means he's doing it wrong... Also, as my car is fully equipped with three pedals, I rarely have both hands on the wheel, especially when driving in heavy traffic.

@FreeMan I said frequently shifting during sharp turns (i.e. the kind of turns that require 180 degrees or so of rotation of the steering wheel.) And, yes, I also frequently drive with one hand unless I'm in a situation where I need either increased steering precision or the ability to make sharp turns. In an airplane, however, I pretty much never use two hands.

You obviously don't have many roundabouts where you are, @reirab . On exiting a roundabout onto a high speed multi-lane road you are both going through the gears rapidly, and turning the steering wheel at least over ninety degrees with precision at the same time. But that this is, indeed, rather difficult kind of supports your original answer.

@DanSheppard Yeah, where I live we mostly have diamond or clover-leaf interchanges for high-speed roads. Not many roundabouts.

Of all the reasons listed in this answer, I feel like the bolded one at the beginning is the weakest, especially in light of the information in @Dave's answer. Particularly: "In a plane the maximum deflection of a yoke is often no more than 90 degrees so having a full wheel (which allows a hand over hand car style turn) is not necessary."

@ToddWilcox The point was that all of the other reasons are directly derived from that one, including the limitation of yoke rotation to 90 degrees (because you can't rotate your wrist farther than that.)

...which the movies always get wrong.  Pilots in the movies either fly the plane with both hands or steer the plane on the ground with the ailerons.

What's this? Two hands on the wheel? please ;)

@reirab discrete* btw

Actually, as I found out on a discovery flight, the yoke doesn't control roll rate--it controls roll acceleration.  If the plane is rolling and one wants to stop rolling once it reaches a certain attitude, one must turn the yoke in the opposite direction to stop the roll.

@supercat Depends on exactly what you mean by "roll rate." The position of the yoke does directly control what I would normally consider to be "roll rate" - i.e. the rate at which your bank angle is changing. (Which is NOT the rate at which the plane is turning.) If by "roll rate" you mean the rate at which the plane is turning, though, you're right. Either way, you're absolutely correct that you don't stop turning just because you put the yoke back at neutral. Instead, you hold the same bank angle (if we ignore dihedral and such) and, thus, the same rate of turn, as the answer describes.

@reirab: From my experience, even after I straightened the yoke, the plane would still keep rolling.  The roll rate may have slowed to zero even without applying counter-rotation, but the plane definitely had some rotational momentum which affected its motion in a way that would only happen with a car if it lost traction.

@reirab: To put it another way, in a car whose tires are gripping the road, setting the steering wheel straight ahead will almost immediately zero out any angular velocity the car would have in the yaw axis.  If a plane has angular velocity in the roll axis, it will reatain it for awhile after alerons are set to neutral.  If one wants to bank to 15 degrees left, one can't hold alerons left until the plane is at 15 degrees bank, and then release them, and expect the plane to stay at a 15 degree bank.  I've less than an hour of time flying, but the above is what I experienced.

@supercat Ah, ok, I see what you're saying now. Yes, the plane will have some angular momentum in the roll axis. At least in the planes I've flown, the dihedral among other things is plenty to overcome that momentum and stop the increase of the bank angle almost immediately upon moving the yoke back to neutral - usually even to the point that some yoke deflection in the direction of the turn needs to be maintained to maintain the bank - but that would vary with aircraft design. Heavier ones would have more angular momentum than what I'm accustomed to. Maybe your plane had low dihedral?

@supercat Of course, it also depends on how sharply you're doing the turns. If you enter and leave the banks relatively smoothly, there won't be much angular momentum, so easier for the dihedral and such to stop it. However, if you just go full left aileron then immediately back to zero upon reaching the desired bank angle rather than a more gradual decrease in the input, then you'll have more angular momentum to stop. And this is assuming you're not flying something like an Airbus where left stick is literally just telling the computer to increase your left bank angle and it then holds it.

@reirab: I think in retrospect I probably perceived the angular momentum as higher than it actually was; for my first turn, I kept the yoke left while watching the artificial horizon straighened out when it reached the desired mark, and the plane kept banking a little.

We Do! It just has been a while since anyone has built a plane like that.
Many early planes did, notably the curtis biplane comes to mind

As closed cockpits came into be and the modern control set up we see something like a car wheel.

The cockpit of the Reliant SR-6A shows the love and skill that went into the restoration.

source
Yokes then evolved to have a more cut down top like the one seen here (in my favorite plane) the Spartan Execuitve This plane was built in the 30's

Even later than that the Ercoupe has a somewhat rounded control wheel.

Also of note the Piper Pacer and Cessna 140 had rounded yokes. After that period most of the big makers moved to the yoke we know and love today. Piper would have a closed top yoke on their early Comanches through the early 60's as well. It should also be noted that early planes (wright flyer etc) had stick like controls. I would assume this was to allow the cable to be mounted far from the pivot for torque reasons although Im not sure (this was for sure before trim).
Remember in an airplane its all about weight so trimming it where ever you can is worth it.
In a plane the maximum deflection of a yoke is often no more than 90 degrees so having a full wheel (which allows a hand over hand car style turn) is not necessary.
Orientation is a bit of a concern when flying on instruments but many race cars have center marks on their steering wheels for a similar reason.
For what its worth formula 1 steering wheels see about as much travel as a yoke and are similarly shaped. Some even have more buttons than a cockpit.

source

And as more and more instruments were added to aircraft, a wheel would just get in the way; you can see and reach over a yoke more easily

@Pondlife: Airbus pilots love the folding table in front of them that the switch to side-stick made room for.

Are aircraft yokes self centering? Or do they stay where you move them to, typically?

@curious_cat that is a complex question as there are many factors involved (more than in a car) and there are many types (and system designs) of yokes and sticks but in general no they are not as far as I know at least when talking about the small planes I fly.

With a steering wheel in a car, the driver can judge how far it is rotated without looking at it by at least three means.
In a car, the driver:

can extrapolate visually the curved path he or she is moving along.
usually experiences centripetal force on his or her body.
feels the feedback of the steering assembly. Whether purely mechanical or assisted, steering assemblies are self-centering. If the driver releases the wheel, it will return to neutral.

In a plane, the pilot:

may be relying on instruments and have no outside cues.
may have a false seat-of-the-pants sense of attitude and direction.
should not need to make violent or large steering movements.
has no need to 'steer' around a corner as you do in a car. Once a new attitude is attained, it should remain stable until the pilot corrects it back to normal (this is a rather simplified statement).

The yoke's shape is valuable because it easily informs the pilot of the yoke's rotation with high precision.

I'm not sure I follow this. Neither 1 or 2 have any relation to whether or not the yoke is centred, and I'm not sure why 4 is relevant either. None of the items in the "in a car" list are relevant to telling whether the wheel is centred.

@DJClayworth the relevancy is that they are cues to whether the wheel is centered.  Using 1,2,3 from the car list you can determine if the wheel is centered or not without looking at the wheel, thus a circular wheel whose orientation may be hard to determine is unimportant.  In the airplane you don't always have those cues, and if you do they can be misinterpreted, thus having a yoke whose orientation is easily determined  is a benefit.

In a plane, even in perfect visibility and not on instruments there are no outside cues as to whether the yoke is centred (unless you are actually looking at the control surfaces).

@DJClayworth in perfect visibility you have a horizon to look at.

@casey ...which tells you absolutely nothing about whether the yoke is centred or not.

@DJClayworth level horizon, no roll rate infers no aileron deflection (assuming perfect rigging, no asymmetric thrust, etc) which means a yoke in a neutral position, e.g. centered.

Steering wheels were developed for cars to provide the large amount of leverage necessary to turn the wheels of a car without any power assist.
In planes, you don't need that much leverage (ok maybe in some long-wing aircraft) to control the elevator and ailerons, and the stick is mostly centered, even in turns.
The idiom for fine control of the yoke is to "milk the mouse", and use two, maybe, three fingers so as not to overcontrol.

Steering wheels were developed for cars to provide the large amount of leverage necessary to turn the wheels of a car without any power assist.   Are you sure?  In my modern car with power steering, it's still well beyond 360 degrees to turn the wheels all the way to the left or right.

I think it would be more correct to say that "steering wheels were of a large diameter to provide leverage before power steering". Power steering has eliminated the need for muscle provided leverage. The only reason trucks & buses have large steering wheels these days is because a small, car-sized one would look weird in the large space of a truck/bus cab. As @MasonWheeler said, it still takes more than a full rotation in most road vehicles to reach full lock, though most cars are only 2.5 turns lock-to-lock.

@MasonWheeler And if the power steering (and power brakes, for that matter) fails, such as an engine stall on the freeway, the average adult will have enough power to steer and brake.

I did say power assist. There are various kinds of assist, only one of which is hydraulic.

It should be noted that a larger steering wheel gives you finer control in addition to leverage.  (Imagine having a doorknob-sized wheel--it would be very hard to get the precise angle you wanted.)

Mason Wheeler: yes, because it uses the same approximate wheel-to-turning ratio as cars designed before your modern car; it has become standard, and people would be confused by a different ratio.  (Not to mention the safety aspect of the power assist hypothetically going out.  I don't mention it because i think car manufacturers don't actually care about that aspect; they don't want to acknowledge that things can go wrong.  cf. www.wired.com/2015/07/hackers-remotely-kill-jeep-highway/

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text:
What permits are needed to operate a human-flying drone in the United States?
Casey in Finland.
If Casey Neistat were to be flown with the human-flying drone in the United States, what licenses / permits would be required from the FAA to make it legal?
All aircraft categories in the FAA assume that the pilot is inside the vehicle. Drones are operated remotely by an operator which is not carried in the vehicle, but drones are unmanned. Is there a regulation for "drones which carry person(s) while operated remotely by an operator"?

I'm guessing something certifying the mental health of the passenger would help, but I'm not sure there are any regulations regarding the craft, its operator, or the operation. It would probably fall under any "pilot-less" aircraft regulations (if any), along with regulations for aircraft that carry passengers. The answer probably lies in the complex combination of many different regulations.

According to https://www.faa.gov/uas/beyond_the_basics/#55:

To fly a UAS that weighs 55 lbs. or more, operators will need to use the existing Section 333 exemption process.

The Section 333 page has further links.  Spot checking some of the approved exemptions shows that the exempted status tends to look quite a lot like the 14 CFR 107 (sUAS) rules and include phrases like "carrying no passengers or crew", "weighing less than 55 pounds including payload".
As far as pilot certification would be concerned, exemption 11422 (which is one I spot-checked with) says:

Under this grant of exemption, a PIC must hold either an airline transport,
  commercial, private, recreational, or sport pilot certificate.  The PIC must also hold a current FAA airman medical certificate or a valid U.S. driver’s license issued by a state, the District of Columbia, Puerto Rico, a territory, a possession, or the Federal government.  The PIC must also meet the flight review requirements specified in 14 CFR §61.56 in an aircraft in which the PIC is rated on his or her pilot certificate.

So, the FAA could decide to issue an exemption under section 333 for such a flight, and declare whatever limitations they wanted (or, of course, reject it outright).  If approved, I'd expect it to come with limitations like:

Must adhere to 14 CFR 107, treating the flight as an sUAS flight even though it exceeds the sUAS maximum weight.
The PIC must be certificated for Remote Pilot (sUAS) or hold an airline transport or commercial certificate with a corresponding class 2 medical and valid government-issued photo ID.

(Every other restriction I could think of is already part of 14 CFR 107, and the carried human would probably be treated equal to a wing walker... and I can't dig up any extra restrictions regarding them)


text:
On average, how often (in flight hours) will a pilot face an emergency situation?
Experienced pilots (e.g. those with over 10,000 hours) are more likely to have faced an emergency situation some time in their career, compared to a new pilot (with say 40 hours). My question is, how often can one expect to encounter an emergency situation (e.g. one every 5,000 hours) ?
Here, an emergency situation is defined as a situation where the use of a "Mayday" call is justified, for example engine failure (in single / multi engine aircrafts), loss of electronic instruments in the cockpit etc. Medical emergencies are not counted.

I feel your definition of an emergency might be too narrow. For example, once the catastrophe began to unfold on AF447, would you describe the situation as an emergency?

@DanieleProcida -- definitely -- loss of all reliable airspeed refs is a Mayday situation for sure

If the FAA released raw data this would be easier to quantify but may be difficult in the current format. Somebody would have to go through all the incident/accident reports and record the hours of the crew. That is if a report was even filed, quite often "emergencies" that end without any remarkable outcome aren't reported, like engine failures in multi-engine aircraft.

What's the threshold for an "emergency?"  As an example, one time I just told the tower the cabin filled with smoke, that I could not see very well, and I was shutting down everything except the LOC and GS receivers.  The next time we talked was on a fireman's handheld. I never used the word "mayday," as there was no time.  Also, I have lost several engines, one once with a FAA Ops Inspector on board, but never told anyone "mayday."

As far as I can remember, none of my situations met NTSB 830 reporting requirements, and generally, the only thing I filed were NASA ASRS forms.  So it is not clear to me what database would accurately report what the OP is seeking.

On a minor point, note that if the aircraft needs two crew members, then the mean frequency for a pilot doubles (or the period is halved) without actual change in emergency event frequency.

On the AF447 situation - it shouldn't have been an emergency. Loss of airspeed indication is supposed to be covered in A330 training: 85% power, 5 degrees nose up, and you hold a reliable cruising speed until the pitot tubes unfreeze. It was aircrew panicking and creating confusion in the cockpit that led to that disaster.

I am voting to close this question—as currently worded—as too broad. The scope of the question could be narrowed to a specific type of operation (e.g.: air carrier or airline ops) for which data may be available. As currently asked, the question invites inclusion of data from operations for which data is not available, such as pipeline patrol operations, and the question is therefore not answerable.

Curiously, in some aircraft (notably some of them with more than two engines), an engine failure isn't even considered an emergency, but rather an abnormal.

Please do NOT close this question. It is definitely answerable and the answer is going to be interesting. Hard to answer yes, off topic/not answerable NO! :-) The other big question site has an answer for this question :p

See "What is the difference between aviation “accident” and “incident”?"

You need to compile some data. I have never had to call Pan-Pan or Mayday-Mayday in 850+ hours of single engine flying. I think good maintenance and flight planning is a key factor in that. And no unlucky occurrences such as a bird strike.

The answer is going to vary wildly according aircraft type, pilot rating and proficiency, number and type of engines, aircraft size, and part of the world.
In this 2016 study by the FAA for GA pilots, the median period of time for non instrument rated pilots was over 3 times as often as instrument rated. 250hrs vs 823hrs. The report describes some of the hardships involved in arriving at the less than precise determination.
I have asked this question to many airline pilots and about half of the 4000-6000hr pilots have a story to tell. Just guessing but I would say modern airliners are perhaps every 10,000 hours.
I must be doing something wrong, because I averaged about every 500-600hrs but then I was mostly flying very old run down Beech-18's in Alaska.

The fact that  they were able to tell the stories is promising. I wonder what the statistics would be on pilot hours as a fatality rate, i.e. 1 fatality per 100,000 hours or something.

Well, having an instrument rating gives you options beyond what you have without one. VFR into IMC? Without an instrument rating, losing all external references is absolutely an emergency. With an instrument rating, you can (not saying it's always the best thing to do) just call up ATC, inform them of the situation, and switch to IFR. Alternatively, you can switch to instrument references only and go back the way you came without significantly endangering the safety of the flight. So it's not particularly surprising that a non-IR pilot would call mayday more often than an IR pilot, on average.


text:
What qualifications or training allow a test pilot to fly a new aircraft?
What makes a test pilot a test pilot? I'd imagine recovery from unusual attitudes is a must, but aerobatic pilots can do that as well. What training does a test pilot go through, that is unique and not taught to general pilots, makes that person a better candidate to test-fly a new aircraft with uncertainty in its aerodynamics?

All commercial or military test pilots attend either a DoD or ABET approved test pilot school.  The military has two said achools: the USAFTPS at Edwards AFB in Muroc, CA and the USNTPS out at NAS Pax River in MD.  There are at least two test pilot schools who train civilian pilots that I know of: The National Test Pilots School in Muroc, CA and Empire Test Pilot School in the UK.
Qualified applicants need to possess at least a commercial pilot's certificate and at least 750 hours TT, plus possess at least a bachelor's degree in engineering, physics, or related technical discipline.  Military programs are very competitive and sought after; TPS slots can pretty much guarantee a job with major aircraft OEMs doing test pilot work after their military service ends.  Outside of the military you will probably need some kind of corporate sponsorship to attend as it is very expensive. The NTPS Masters of Science in Test piloting in an 11-month course costing a whopping $960,000 to attend!
The courses in a TPS are graduate level type classes.  The NTPS curriculum can be found here.
Hollywood portrays test pilots as these outlandish, devil-may-care guys with brass balls and ice water running in their veins, but the truth about most test pilots and flight test work is pretty boring by comparison to the movie image. Test pilots are first good system engineers, second skilled aviators and third calm and collected under pressure. Test flying itself is much more about planning - and planning for contingencies and contingencies for those contingencies  - than the actual flying itself.  Test flying is conducted according to more or less a rigid schedule developed by a flight test department.  A test pilot will fly the aircraft through specific test points and is expected to maneuver the aircraft in a very precise way - precise control inputs, precise altitudes, air speeds, angle of attack, flight maneuvers, etc. In order to collect test data for the flight test team.  The test pilot is also expected to be able to correctly evaluate how the aircraft or systems handled.  Also needed is an ability to accurately describe discrepancies in performance and handling to design engineer teams to correctly determine the root cause of these issues and address these problems correctly.
Safety is also paramount for doing flight test work.  Long gone are the days of strapping your little pink fanny into a crate, pushing it off a cliff and hoping for the best on the way down.  Test plans are thoroughly evaluated prior to flight for risks, mitigating factors and means to minimize those risks - and contingency plans should something go wrong.  I once heard a USN test pilot put it "we try to make the process as boring as possible."  Many test points will be attempted in simulators prior to the actual flight test and test pilots will have flown them many times, complete with conducting emergency procedures there.
Most test pilots don't even do experimental work; often times they are involved with manufacture flight test work.  This is usually involves simply testing all the systems of an existing production sample aircraft.  Other jobs test pilots are involved with are testing of new avionics, weapons, or mission systems aboard existing aircraft as part of the approval process for its use.

"most test pilots and flight test work is pretty boring by comparison to the movie image." Indeed. the only test pilot I know personally has "fun" tow-launching gliders with a fairly ancient fixed-prop light aircraft at weekends - and "serious fun" is flying aerobatic displays in a WWII Spitfire. (Though he damaged his reputation for "cool" a bit when he forgot which side of the cockpit the Spit's hand brake lever was installed, pulled a similar looking lever on the wrong side, and retracted the undercarriage while taxiing after landing - OOPS!)

For certification of flight simulators, some subjective tuning needs to take place by a type certified pilot. Both for military and civil aircraft types, the difference between a line pilot and a test pilot is the much deeper understanding of the latter of the physics behind all processes. They are flying engineers.
This link is the test pilots notes for the F-104 Starfighter. A distinguished fighter ace and super-pilot such as Chuck Yaeger hints in his autobiography that test pilot school was not exciting: too much theory.


text:
Who first coined the phrase "aviate, navigate, communicate"?
The phrase "aviate, navigate, communicate" describes the priorities of tasks for a pilot. It is applicable to a wide variety of situations, including military scenarios and emergencies.
Who first introduced this phrase, and when did it first appear in the aviation community?

I don't know the genesis of the phrase, but I heard several WWII era military pilots interleave it with stories of their sorties, and of the debriefs for those sorties.  Based upon that, I would say that the expression dates back to at least the early-1940's.


text:
How is spilled fuel cleaned up at airports?
In an accident where an airplane leaks fuel onto the ground, how is it cleaned up?

Depending on the quantity, jet fuel can be cleaned up by use of a sump truck and dry absorbent material or if permitted by the airport and local environmental regulations, the fire department can spray water to wash it down the storm drain.

Both seem perfectly reasonable. However, they would seem much more legitimate if you had some regulation and/or legal references.


text:
Can Obstacle Limitation Surfaces Change over time?
I want to know whether the OLS (Obstacle Limitation Surfaces) around an aerodrome can change over time?
I know that if the ground level was altered this would change the limits of each surface.
However, my line manager told me that obstacles cannot change the OLS, and has stated that the answer is quite obvious. But I am still in training and still rather confused about it. I work in Safeguarding, so I've done some research so far, but I haven't found a decent answer from searching online.
Could I have some guidance please?

Is your manager making the distinction between an envisioned (mathematically constructed, not physical) surface, and any obstacles which penetrate that surface? Adding an obstacle wouldn't redefine that surface, although adding or lengthening a runway might, depending on how the surface is defined.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Plane suddenly descending nose down, was it normal?
I was on flight FR8710 Vie-SUF on 2023 May 1st, and the descent was quite abrupt, at least according to my standards (and to the other passengers' ones). I fly pretty often and this was the first time I experienced something like this; the flight was overall smooth until the plane suddenly "dropped" nose down for more or less 5 minutes. I can't remember if this was anticipated by a "prepare for landing" or similar announcement; usually I feel the smooth transition when the engine power is reduced, this time it was like a sudden unwanted uncomfortable undesired change in speed and tilt.
I felt really uncomfortable, and many around me confirmed they had similar feeling. It looked like the flight attendants had to suddenly rush operations and they did not look calm either. Now, SUF is not a really busy airport, the weather conditions looked fine, and no one was really expecting that.
Is there a way to understand what happened or if anything was just normal? Is there a way to understand if anything was filed regarding a procedure different than usual? I am no aviation expert (really far to be one actually) and I would really appreciate if anyone could give a hint here. From flightradar24 I can see the difference between a "normal" altitude drop and the one experienced in this flight.
I have checked previous similar questions on the StackExchange and learnt from the answers but they did not satisfy all my curiosity about the conditions I experienced on this flight, I hope you can help.
Edit: if I read the graph correctly (and we assume the data is accurate), between 6h24'33'' and 6h28'08'' there's a change in altitude from 33150 ft to 15800 ft, meaning ~4842 ft/min?!?
Thank you

https://aviation.stackexchange.com/questions/8289/what-is-the-normal-descent-rate-for-airliners

Thanks, I have seen this but I cannot still understand what justified a descent of ~4842 ft/min

The flight was running late. Maybe they just wanted to get there faster?

Thanks, my question was specifically: is that "normal"? Is it considered normal in aviation to go 5000 fpm if the company/the pilots are in a hurry? I've read over 3000 fpm it starts to be very uncomfortable for passengers. There has been some news these days about a Boeing 737-Max that plunged from 4,425ft to 2,300ft in just 17 s (7500 fpm if data is correct), and they opened an investigation over this incident.


text:
What is the exact process to request an N-Number change while registering a purchased aircraft?
I just purchased an aircraft and have the Bill of Sale form signed by the seller. I understand that I need to submit the bill of sale (AC 8050-2) along with AC 8050-1 form to complete the registration.
The seller of the aircraft wants to keep the N number. I requested a new N-Number from the FAA website and the reservation is still pending. I see that the N-Number change is done using a letter to FAA requesting the change as described in https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/special_nnumbers
What is the correct order of submissions in this scenario? Do I send the registration form (AC 8050-1 with Bill of Sale 8050-2) AND the letter requesting N-Number change together? If yes, do I use the old or the new N number in the form AC 8050-1? Also, how do I make sure the old N-number is reserved back to the seller?


text:
Calculating Lift-To-Drag ratio of a rotating propeller with zero forward velocity
I'm simplifying some blade element theory problems by assuming that the propellers are perpendicular to the ground and their motion is constrained to being purely vertical (without forward velocity).
Im having some trouble calculating gamma, which is the arctan of the coefficient of drag divided by the coefficient of lift. This is related to the lift-to-drag ratio, as it is the arctan of its inverse. This gave me the idea to use lift-to-drag equations (like total drag = induced + zero lift) for finding gamma
However, lift-to-drag ratios are typically used for things like aircraft blades and not rotating propeller blades. Since the motion of the blades is contributed entirely by the blades rotation (no forward velocity), Would it be possible to use these equations if I assume the tangential velocity of the blade to be the equivalent airspeed in the equations?

I think this answer is what you are looking for.

Are you working from a particular resource when writing your BEM?  It might be easier to point us at a particular equation with a given set of nomenclature.  When a BEM talks about cl and cd, it usually is referring to 2d sectional lift and drag coefficient -- not the combined coefficients of the propeller as a whole.  The BEM works very logically through the process of finding the velocity and angle of attack at every blade station.  That is the whole point of the BEM.

@RobMcDonald Im not working from a particular resource, per se, im trying to calculate the effective lift and drag coefficients of a propeller from APC propellers given their documented performance and geometry data (which dont include Cd and Cl sadly).

We don't normally book-keep propellers as having an overall lift and drag coefficient -- most of the time, that is meaningless.  We typically care about a propeller's thrust and power coefficient.  What are you actually trying to accomplish?  Why do you think you want lift and drag coefficient of a propeller?


text:
What are the duties of an ATC supervisor?
We know that each air traffic control facility has a "supervisor", a person who is "in charge of the controllers", so to speak.
What exactly are the duties of the supervisor? Here are some of the things I've guessed:

Resolve conflicts between a pilot and a controller (by assigning a different controller to the position? Taking over the radio directly?)
Assist in emergency situations (coordinate with nearby airports / approach sectors?)
Deciding when to merge / split sectors, when to bypass noise reduction procedures due to weather etc.

Am I correct?

I can very easily see #1 getting outright dangerous very quickly. You don't just replace someone in a high-stress situation and have everything instantly work out. And of course the pilot doesn't report (in the managerial sense) to anyone in ATC. It's generally in every pilot's interest to comply with ATC, because ATC has the "bird's-eye" view of their airspace which each pilot can only observe a narrow cone of, but the pilot still has the choice of exercising their authority over their aircraft if in their judgment doing so is required to avoid or to deal with an emergency situation.

For which country are you asking?

In the FAA, there are two types of "supervisors" who might be on duty at any given time: a genuine managerial supervisor, who is part of the managerial pay scale and is not part of the bargaining unit (union); or a "controller-in-charge," a "line" controller (a bargaining unit employee) who has been certified to perform most but not all supervisory duties if a supervisor is on break, not scheduled that day, etc. Sometimes the supervisor or CIC will be working a control position, or they might be working at a desk in the back of the operation not talking to any aircraft directly.
In either case, the general duties of the supervisory position are:

Running the shift (determining the break schedule, approving sick leave, etc)
Assigning controllers to combine or decombine control positions as traffic and complexity warrant
Assigning on-the-job training to ensure trainee controllers get sufficient training time
Monitoring the operation and, if they feel it is necessary, instructing a controller to take a specific action to ensure safety (this happens very rarely!)
Coordinating with surrounding facilities—not about individual aircraft (the controller on position does that) but about traffic management initiatives, contingency situations (e.g. telling people "we lost commercial power so we're on generators, be prepared in case we lose those too"), etc
Answering the commercial phone if people call (survey pilots informing where they will be operating, military ops calling to see if a plane can come do practice approaches, someone claiming they saw a UFO, noise complaints, etc, etc)
Keeping the daily log up to date (logging equipment outages, runway closures, etc)
Coordinating with other facilities or airport operations regarding emergency aircraft or crashes

The CIC authorized to carry "on the spot" corrections—telling the controller on position they need to do something else for safety reasons—but is not authorized to perform personnel actions like officially counseling a controller about a loss of separation. That's reserved for the actual supervisors.
Of note, if you hear a controller give an instruction and then another controller comes on the frequency and gives a different instruction, that isn't a supervisor. That's the instructor plugged in alongside their trainee controller. During training the certified trainer controller is responsible for the position, so they will give their trainee latitude to make their own mistakes but will step in to prevent an actual safety event.

Nice answer! When a "tower supe" is needed in order to Line Up & Wait, is that a CIC or is that something else?

@RalphJ we don't use LUAW at my facility but looking at the 7210.3BB, 10–3–8 a.4 and a.6 only say that both the local position and the sup/CIC position must not be combined with any other positions. It's a requirement that the position be staffed, by either a sup or a CIC.

So then in practice they'd also need a Ground controller, since that couldn't be combined with Local?  Thanks for the insight into the world I talk to often but rarely get to visit!

That is a very complex question. What do you mean with ATC facility, exactly? ACC, sector control, approach or something else? Their operation will depend heavily on the type and if it is US, EU or somewhere else.
I can tell you, that there will not be any conflicts between a pilot and an air traffic controller, everybody is very professional, if a pilot really does something wrong or does not comply, a report will be issued, after the fact.
An ACC may receive an emergency call and re-route the plane accordingly. But typically they won't handle emergencies, as the vast majority happens during take-off.
En-route conflicts will not occur in a managed sector, if there should be one unexpectedly, the pilots are responsible, as a last resort you have the TCAS. At least in europe, that is the order of precedence.
Sectors are split according to a fixed plan. Controller roasters are similar to pilot roasters. You can't change them on a whim. Controller workload is watched closely. Also the errors they may make.
Noise reduction is a concern of SIDs/STARs (the routes close to an airport) of the given TMA and they are not in the purview of either an ATC controller or supervisor. They are issued after a lengthy process by the ANSP.
This is a general answer for the situation in EU/US. Things may be different elsewhere.
The ATC facilities:

Tower
In a tower, the supervisor will usually
 - ensure safe conduct of the watch
 - check flight plans, slots, etc
 - liase with centers, cfmu, airlines, etc
 - handle, support, supervise emergencies
 - day-to-day management
 - controller management (breaks, time, etc)
Depending on the airport controllers will occupy a wide range of positions.

Approach
Approach is typically a different facility, that is colocated and has their own supervisor. The tower supervisor will coordinate with the approach supervisor.

ACC
The ACC has similar duties to a tower. The difference is, that the positions are for one sector, there are much more positions. There may be two controllers per sector. You will then have 1-2 "supernumerary controllers" for X controllers.
Apart from that you will have a number of assistants and other personnel for a variety of duties.
In an area control center, the supervisor will ensure, that all this works well together, so much more responsibility.

Situations

taxiway assignment
In this situation, we are in the tower on ground control. There is not much a pilot can do other than follow the instructions. Sometimes they have to wait, sometimes they are forgotten or they loose their slot. Sometimes the lineup is slow, there are a number of things that could happen.
It should be noted, that most airports have a departure management software to de-conflict aircraft management. Most pilots know that.
Here a supervisor might go and ask, if a plane can be squeezed in, if it lost its slot.

speed / altitude
In controlled airspace, a pilot will follow the instructions to the letter. There might be communications issues, "climb to" / "climb trough"
If they don't comply here, that would be a major issue and would trigger all sorts of alarms. It could ultimately end with two fighter jets next to the aircraft...

plane crash
The controller would handle the aircraft and emergency services, the supervisor will call approach, they will divert all aircraft, most likely back in stacks, then he will close the airport for traffic. Every airport has an ATIS, the message there would be updated. Then the ACC is informed and also cfmu/network manager.

I read this answer over and over again, and I am really having trouble understanding it and how it addresses the question. Re 1: conflicts do happen, especially in busy airspace. A report is filed later, but something has to be done on the spot to resolve it. Re 2: An aircraft can declare an emergency anywhere and at any point in time. And no idea what TCAS has to do with an emergency. Re 3: A noise reduction policy may route planes to land with non-precision approach or less favorable wind.

Re 1: In europe capacity planning is such, that the planes are deconflicted before even taking off. Afaik, the same is true in the us.
Re 2: Yes, an aircraft can declare an emergency at any time. I rephrased it. But they typically don't have them en-route.
Re 3: SIDs/STARs are very strict, the pilots fly them as they are in the AIP. Once a ACC is responsible, the plane is already in the upper airspace and noise is not an issue anymore.

That's what I don't understand in your question. Noise, emergency and such are typically handled in a Tower or Approach. Most emergencies happen during take-off. Some time during/after the climb-out they are handed off to an ACC. Noise will not be an issue anymore. And like I wrote before, when an AC is en route it is de-conflicted, they fly their waypoints and that's it. In my opinion, you need to be more specific about the situation you are taking about.

I think we are having very different interpretations (maybe I should edit to clarify). Re 1: I meant conflict like, an argument between a pilot and a controller, such as taxiway assignments, speed restrictions, altitude restrictions etc. Usually the conflict arises due to being inefficient / waste of time to at least one party. Re 2: say a plane crashed on landing. The tower controller is busy coordinating rescue units, and somebody has to alert approach to stop sending planes to that airport, then somebody has to alert whatever it is further up the chain.

I think I know the disparity now: by "air traffic control facility" I mean a location which provides ATC service: clearance, ground, tower, approach, departure, en-route etc. While it appears your definition is en-route only.


text:
How much water is carried for jet engine water injection?
An answer on a related question stated that water injection was used on some of the early jet planes, for example Boeing 707 and Boeing 747-100/200.
I presume the water is stored in some tank. How much water is typically carried for this? And given the water flow rate, what is the usual water injection time available before water runs out?

This paper here gives a good overview of water injection.
It suggests for injecting water into the compressor, a 300 gallon tank is necessary, for a 2.2% water to core air flow ratio (the historical norm), for injection from take-off to top of climb.
For injecting into the combustor, it suggests a 135 gallon tank, for a 0.5:1 water to fuel ratio, again for injection from take-off to top of climb.
For both of these scenarios, the tank water flow rate was designed to achieve a 50% NOx reduction. The paper gives other water quantities required to acheive different goals (eg different NOx reductions and different turbine temperature reductions).
I don't think the paper indicates how long it takes to get to top-of-climb. I assume these are US gallons, as its a US paper.


text:
What is the procedure for handing over controller positions to the next shift?
I'd like to know how a controller of the previous shift hands over the position to the person of the next shift.
I imagine the next person should be present at the console for at least X minutes, so he or she knows what is going on. Is X defined by some regulations (or ICAO recommendations), or is it completely up to the ATC facility to decide?
Is sitting next to the console enough? Or, should there be some sort of briefing (by the current controller / supervisor)?
(Note: I don't want to tag this to a specific country. I am interested in whatever country the answer applies to.)

@CGCampbell I'm looking for a general answer. Even if it differs around the world, there should be a common set of principals which they share, unless the answer is "it differs so wildly around the world that an answer would be too long"; or if we have like 10 different answers to 10 areas in the world.

I've asked an ATCO friend of mine who is in Greece in area control center and he told me is that there are no regulations; only good practices. For example, since for each sector you don't have one but two controllers, you don't change planner and radar operator at the same time. You might switch them 15 or 20 minutes apart. The supervisor is not involved in the process (there are several positions changing at the same time, who should they attend first?) and besides they are already busy with bigger things.
The current controller will need to brief the next one only if there is something unusual. Otherwise, the controller knows what sector they will take over and the sector peculiarities. Glancing at the current traffic will give them a good picture of what is going on. The relieved controller can stay next to the one who relieved them as long as they want but again, there is no time specified by regulations. But usually one or two minutes is enough. Usually an informal "Joe can I go? Need me anything else?" is enough and in the vast majority of cases the response will be affirmative.
This is specific for the Hellenic ACC, I don't know what happens in approach or tower positions although I have a feeling that things are not extremely different.


text:
Do pilots land a helicopter sideways for improved visibility of the landing area?
When flying helicopters in the PC-based game Arma 3 (not a flight simulator), some of the cockpit have a large instrument panel directly in front of the pilot, obscuring the view of the ground ahead when flying low. However, the cockpit has excellent visibility to the sides.
One of the technique to achieve a precise landing is to land not forward, but sideways. For example, let's assume the pilot is seated on the right, and the helicopter is heading North and approaching a landing target from the South. When the helicopter is approximately 50 feet from the landing target, the pilot swings the helicopter to the left by applying left pedal, pointing the nose to West while keeping the helicopter travelling North. The pilot then completes the landing by looking to the right.
Is this technique valid in real world helicopters?

No.  Often helos use windows on the floor of the cockpit near the anti torque pedals, which allow a pilot to look directly down at the landing area, as this example of a EC130 shows.

Helicopter pilots seldom land at a sideways angle, save for landing on slopes terrain or a situation required to fit the helicopter into a space.

One of the main reasons we do not land sideways is the chance of catching a skid on something (rock, terrain, etc) and rolling the helo over....


text:
If everybody jumps in an airliner, would the pilots notice?
I often have this thought when stretching my legs on a long haul flight: jump up and down in the cabin and see whether the pilots complain. Alone, it is unlikely my weight would have any noticeable impact on the plane's attitude, and I'd likely annoying some flight attendant or passenger around.
But let's say I manage to get all passengers on the flight to cooperate. Everybody jumps up pretty much the same instance (within reasonable human reaction time). Will the pilots notice its effect?

You'd get a more noticeable and interesting effect, in my opinion, by having everybody walk to the rear as quickly as possible and then crowd there. Then after say, 30 seconds, everybody walk forward and crowd there. Repeat as necessary. When I was flying Fairchild F-27s, we had a very heavy prankster pilot who, when deadheading, would do this. And just on his own, it would force us to retrim.

@fooot woh I've been on this site for quite a while now and never saw that question!

30000 lbs of people leaving and landing on the floors at the same time?  They'd notice something.
Physically, the weight of the passengers on the floors would increase a bit as they pushed off and accelerated vertically.  Maybe 30000 lbs would increase to 35 or 40000 lbs for a split second, then once everybody's feet are clear, all the passengers are basically in a ballistic arc, so their weight is removed from the floors and the airplane is now 30000 lb lighter for a split second, then they would land and their vertical acceleration would apply maybe 40000 lbs to the floors for another split second, before returning to the steady state 30000 lbs.  So I would say it would feel to the flight crew like they hit a very small bump of turbulence, and there were be some kind of dull thud coming from behind from 300 feet landing at once.

Also, they‘d probably physically notice the shudder in the structure...

They'd also hear it as well https://youtu.be/yjbpwlqp5Qw?t=1m

So... I wonder if they did this at take off, could they cause a stall? I've read answers on here about foolish skydive instructors 'pranking' pilots by suddenly moving the team aft to cause stalls

That's what I meant by thud and bump.

@cloud no. It would be equivalent to a minor turbulence encounter.  Now if all the pax ran aft and crammed themselves into the back, phonebooth packing style, then it could get exciting for the crew.   Re skydivers, if I was a jump pilot and a skydive instructor did that to me, he wouldn't be a skydive instructor any more.  Now my dad told me long ago that when he was flying C-47s in Burma in  WW2 his kicker crew would move forward and aft on the trip home to change the airplane'

's trim, just to be annoying.

@JohnK Haha, I guess during wartime you gotta have fun. Read the top answer to this question and see if you can sustain your belief... https://aviation.stackexchange.com/questions/2507/can-passenger-movement-in-an-airliner-make-it-stall/3074#3074

@Cloud that story is pure BS.  Besides the crazy irresponsibility of it, the obvious clue is "tailgate".  Airplanes with cargo ramps don't have "tailgates"; they are "ramp doors" or "cargo ramps" something similar.  You have a tailgate on a pickup truck.  Only someone who has never been near one in the first place would say tailgate.

@JohnK Thanks for clarifying John. I have my first jump soon and was hoping not to have instructors intentionally stalling the plane, even if it was at "well over 1,000ft"


text:
How to escape from a pressurized airplane?
Saudia Flight 163 was an airplane where all passengers and crew onboard died following a cargo fire. The plane managed to land safely, and the passengers had moved to the front of the cabin. However, it is stated that:

It was noted that the doors could not be opened because the pressure was not equalized [1]

Why was the cabin pressure higher than outside?
As a passenger, how could you escape an airplane that is pressurized, such that the plugdoors will not open?
If you are outside of the aircraft, is there any way of opening it?
[1] https://www.aviationfile.com/story-of-saudia-flight-163/

The doors of an airliner are difficult to impossible to open while the aircraft is pressurized significantly higher than its environment. In this specific incident, the aircraft was pressurized because the outflow valves were nearly fully closed, and the engines (which provide the pressurization) were still on for several minutes after the landing.
As a passenger, there is very little you can do. Consider that anything you can do to depressurize the plane on the ground is something you could do to depressurize the plane in the air. Something the airlines naturally don't want you to do. You could try flushing the toilets, which would relieve at least a little excess pressure, as long as the engines are off.
The cabin crew can depressurize the plane by shutting off the engines and opening all the outflow valves. (Though in the L1011, a loss of electrical power would have kept the cabin crew from doing this). Ground crews may be able to force open the outflow valves or possibly smash a window or cut into the fuselage if that doesn't work.


text:
Turn Coordinator Behavior During Rollout - Sheppard Air Question on Coordination
The question and given answer are:

While rolling out of a left turn, if the inclinometer appears as
illustrated in A, the HCL (horizontal component of lift) and CF
(centrifugal force) vectors would be acting on the aircraft as
illustrated in:
A) 4, and more right pedal pressure is needed to center the ball.

[Figures below show: The inclinometer ball is to the right and the force vectors they selected are small HCL to the left and high CF to the right.]
If the question stated "during a sustained left hand turn" I would 100% agree. The ball is to the outside and you are skidding - too high of a yaw rate (high CF) is offset by a low bank angle (low HCL).
However, during a rollout, your inside (left in this case) aileron is creating more adverse yaw due to the downward deflected aileron. Therefore, although you are exiting a left hand turn you are effectively "slipping" to the right if the inclinometer appears as it does in (A). You need more right rudder to create more yaw to offset your downward deflected aileron. Since your yaw rate is lacking (low CF) and you are rolling right I claim the correct vectors are number 2.
I can't quite wrap my head around the right frame of reference here, or how gravity and centrifugal force come into play during rollout. What is the correct answer and why?

After writing this question and thinking a little longer I think I may get it. The downward deflected aileron is in effect doing the same thing as if I had applied too much inside rudder. Therefore, during the rollout you can have an aileron-induced skid. Doesn't matter that you are rolling right because your lift vector is still pointing left (and up) and therefore so is CF. Still hoping to hear some of your thoughts!

Exactly as you say with an aileron-induced skid. The centrifugal force (not centripetal force) is opposite the direction of the turn. So the horizontal component of lift is to the left and the centrifugal force is to the right.

You're in a left turn and the ball is to the right. This a skid, not a slip. You have decreased your angle of bank but not decreased your yaw rate enough to compensate.
The ball is feeling the forces shown in the diagram. The ball is to the right, so the force pointed right must be bigger. Therefore the answer is 2 or 4. You're in a left turn, so the horizontal component of lift (which is what lets you turn in the first place) must be to the left. So the only possible answer is 4.

Don't have enough reputation to upvote but I think I understand!

@codenoob Welcome to the site! Feel free to ask for clarifications if anything is unclear. Even with no reputation you can mark an answer as accepted by hitting the checkmark next to it- but I usually recommend holding off on that for a while to see if you get any better answers.

Thanks! Longtime reader. I'll wait and see if anyone else is working on something.

Well, do you learn how to fly after reading a book, or do you write the book after learning to fly?
It may be a bit of a trick question but ... if one were flying in a coordinated manner, why would one just roll out of a turn?
Wouldn't it make more sense to exit the turn with both yoke and rudder and stay coordinated?
It seems you've figured out that the lower aileron will create adverse yaw, and rudder must be applied to compensate.

step on the ball

But the important lesson here, especially when low and slow, is not to be uncoordinated when turning, especially with the inside aileron down.
If the inside, lower wing stalls, the plane will roll into the turn.  At pattern altitude, it is generally non-recoverable.


text:
FXE depiction on VFR sectional - why are there two "beacon stars"?
The airport symbol for FXE (Ft Lauderdale Exec) has two stars for "lighted beacon" on the Miami sectional. Why is there a second star?
There are also two identifier labels for the airport.

The Miami Terminal Area Chart only shows one star / label for FXE.
Additional info: The "double star" / "double label" is also visible direcly from the source on the FAA's VFR Raster Charts (both TIFF and PDF versions), so I don't believe it is a SkyVector thing.

Usually this is because the airport is right on the edge of two different sectionals, and the way SkyVector stitches them together you see the info from each one. In this case FXE is right in the middle of the Miami sectional, and the double info appears as depicted on that one sectional. Could be worth submitting an Aeronautical Inquiry about.

Thanks @randomhead - I just submitted an inquiry. I'll update if/when I hear back!

My foreflight map show double stars in wide range mode, but if I zoom up the map, it only shows one star at the bottom. I guess it’s just a problem of map resolution

@Shin you're just restating OP's question. The sectional shows two stars while the TAC only shows one. (It's not a question of "resolution" as such. Foreflight just automatically switches to the TAC when you zoom in far enough.)

@RalphJ The FAA has VFR raster charts available in TIFF and PDF, and both versions have the "double star" and double label. Also, it's smack dab in the middle of the MIA sectional as randomhead pointed out.

Do you have a paper sectional?

@MichaelHall I do not own a paper MIA chart, but the raster charts which I linked to are official FAA charts.

i don't doubt that they are "official", just wondering if you had a way to verify Randomhead's theory.  Because them being raster charts is likely why.

@MichaelHall The paper charts are just printings of the raster charts. They aren't printed by the FAA or anything so there's no reason to think they will be any different.

@MichaelHall just to be sure of what the others are saying I'll try and get my hands on one! Would be interesting to go back to previous publications and find out when this anomaly started, assuming that's what it is. Too bad I don't think FAA has archive of the raster charts (someone correct me if I'm wrong on that)

Ok, I'm just saying that there's some weirdness at the intersections of charts, I've seen it myself on electronic charts where Sectionals meet a TAC.  This seems like the most valid explanation to me, and worth investigating.

Is the paper chart meant to be a top-half / bottom-half, printed on opposite sides of the paper? If FXE is near that edge, perhaps the info is duplicated so that one prints / is visible when viewing the "top half" side of the chart, and the other for the "bottom half" side? Without seeing the paper chart, I'll spitballing here.

The recto-verso error makes sense as when an aerodrome has actually two beacons (e.g. O22 or UKI), it still appears with a single star on a sectional chart.

OK, so here's what I found. As people mentioned in the comment, the KFXE is depicted on near the bottom half and top half of the sectional charts. One has a star on the top of the airport icon, the other does on the bottom of the airport icon. However, I can tell both of them has two stars apparently...
North half:

South half:

Is it like "top half of chart" on one side of the paper and "bottom side of chart" on the backside? I don't have any VFR charts handy so I'm not 100% clear why Ft Lauderdale is near the edge of the paper.


text:
How frequent is the use of spoilers during descent?
Having flown a number of flights as a passenger recently, I observed that:

Roughly 50% of pilots used spoilers above FL180
Almost everybody used spoilers to pass the 10,000 feet / 250 knots mark
Roughly 25%~33% of pilots used spoilers around 7,000 feet ~ 8,000 feet down to glideslope capture

Are modern airliners so "slippery" that an engine-idle descent is not enough to meet operational requirements? (on the other hand, makes them really good gliders in the event of a total engine failure!)
I was told that companies like to use engine-idle descent as much as possible because it is the most fuel-efficient way to get down; spoilers are only "sometimes" used when ATC clears the descent path unexpectedly, which usually means a short-cut and passengers can expect an earlier arrival. That was in the 90s'.
Has it changed in the last decade? How frequent is the use of spoilers during the descent portion in today's flights?

Out of curiosity, how do you observe the altitude when you're a passenger on an airliner? Are you checking an altimeter on your phone?

@yshavit the new Android-based onboard entertainment system has many new functions, including a PFD-like screen which shows speed, altitude, v/s, heading, winds aloft, pitch & bank. The altimeter on a watch or phone would only measure cabin pressure, which never correspond to the atmosphere pressure outside.

Derp, of course. Silly me. :)

@yshavit and on a clear day, you can have a decent idea by looking out of the window... the 10,000ft/250 kt point is also typically marked by the cabin seatbelt signs being turned on, too, which gives you a nice point of reference

@kevin: "which never correspond to the atmosphere pressure outside."  Only if your airliner is pressurised; lots of smaller propliners are unpressurised (they have to stay below 10 kilofeet AMSL as a result, but this isn't really a problem for propeller planes on short hops).

For me, it depends on the plane. On the A320neo, (in MSFS) I do it basically all the time. But on the B747i, only when the plane is already on the ground. Because it's a super heavy aircraft and when the engines are not at full power and the spoilers raised, it will stall.

Very frequent.
Modern airliners are certainly fairly slippery, but it's not so much that they're super-gliders that we can't wrestle down onto the ground.
It's more a function of busy airspace than a property of the aircraft. When you remove power from any aircraft, it's going to descend - the only question is the rate. I promise you that if you found yourself a long way from an airport in a powerless B737, you'd find that descent rate to be faster than you'd like!
The main reason for spoiler use isn't that a modern aircraft glides "too well" - but rather than the airspace is busier so aircraft are expected to respond a little quicker than in the past, which can make it more convenient to descend faster as a pilot. It also means that ATC will often ask pilots to maintain a higher-than-ideal airspeed on the descent: if travelling at 160 knots, you'll descend faster than you would at 180 or 200 knots, for example... but more often these days, you're asked to maintain a higher minimum airspeed for longer. That's often convenient for ATC as it gets you where you're going faster, and it's convenient for you too, because you get to go home faster: but it means you're travelling a lot further in the next minute, making it harder to hit the descent rates required, necessitating the use of spoilers in some circumstances.
Clarification: In this answer I've focused on the later stages of the flight: "Slower = descend faster" is not necessarily a universal constant - aircraft glide best at their "best glide speed" which is a function of drag, weight, and airspeed. This answer assumes that, as for most airliners, best glide speed is in the region of 200-250 knots, and that an airliner is unlikely to descend at/faster than their best glide speed in the approach phases where speeds are typically in the 150-200 knot range.
At lower altitudes when descending under ATC, the above ATC-centric discussion applies. At higher altitudes, it tends to revolve around efficiency and company policy: the longer you can stay at cruising speed/altitude, the more efficient your flight will be: therefore it saves the airline money to descend as late as possible, requiring a higher descent rate. Spoilers, of course, help with that.
TL;DR: Some of it stems from the aircraft design being more aerodynamic and therefore better at gliding, but it's more closely related to ATC being busier and therefore keeping aircraft higher/faster for longer, which requires higher descent rates and therefore the use of spoilers, along with the fact it's more efficient to stay high/fast in the cruise for as long as possible then descend later/faster

Can you please clarify the slower speed - higher descent rate statement you make? It seems to contradict other answers stating the opposite .

@SteliosAdamantidis I'm not sure where that answer contradicts mine? They discuss entirely different concepts. An aircraft will glide "best" (in terms of altitude lost per unit of distance) at the best glide speed: typically 200-230 knots in most airliners (A330 is ~210 knots, ~220kts for a 767, ~200 kts for a lighter aircraft like an A320/B737). This answer is discussing slower speeds, though and is relating to altitude loss per unit of time (which isn't necessarily synonymous with altitude loss per unit of distance) I think you're possibly confusing different concepts between the two answers

There's a hidden assumption here, but I have some problems naming it. One clear counter-example is that in a straight nose-down dive, going faster means descending faster. More in general, going faster at the same AoA means more lift and thus a slower descent/faster ascent.

@MSalters you're getting into aerodynamics, not airliner operations, and outside the scope of this question. If your A340 is in a nose dive, you have significantly bigger problems than whether your spoilers are deployed. We're talking about deploying spoilers in a constant airspeed descent, or when slowing in the descent, during normal airliner operations.

@MSalters The "hidden" assumption is that he's talking about descending alone (while preserving other flight parameters), not trading height for speed. Such exchange is useless when you want to land.

@Agent_L - I see where you're coming from, although I didn't see that as a hidden assumption, but rather one implicit in the question in that it relates to airliners (as opposed to aerobatic or combat aircraft)

@JonStory Neither it was hidden to me. I edited my comment.

I refer to the section where @casey mentions Often the choice is descend or slow down while you mention if travelling at 160 knots, you'll descend faster than you would at 180 or 200 knots, for example

@SteliosAdamantidis that isn't a contradiction?

Yes it is a contradiction, that's what I'm saying. You say lower speed results to greater descent rate, @casey says you will either increase your descent rate or decrease your speed (i.e. you can't do both). Anyway since I believe we abuse the comments, I will post a new question. This out of the scope of How frequent is the use of spoilers during descent? question anyway.

It really isn't: that answer talks about deceleration, mine doesn't? At no point in my answer is an aircraft required to both descend and decelerate

@MSalters going faster at the same AoA means you fly a turn. Or aerobatics. More lift means more load factor, not a climb.

@John Story At no point in my answer is an aircraft required to both descend and decelerate But is that not the whole reason for using spoilers/air brakes - to descend faster and decelerate simultaneously? Your optimal glide speed gives you the shallowest descent angle. If you need a steeper angle you have 3 choices: 1) pitch up - your airspeed goes down, but sink rate goes down also. 2) pitch down - sink rate increases, but so does airspeed. 3) spoilers/air brakes - less lift and extra drag, airspeed goes down, sink rate goes up.

@TomMcW I don't understand what you're asking, is that not covered in the answer? When you want to descend faster, deploy spoilers to both descend faster and avoid acceleration/to decelerate. Spoilers help you lose airspeed and/or altitude, but you can lose either while gaining the other, lose one while the other remains unchanged, or reduce both at the same time... The balance is entirely independent of spoiler deployment, the spoilers just make you more draggy with less lift

I too think there is a contradiction here somewhere. Higher speeds equals bigger altitude loss per time, but not necessarily bigger altitude loss per distance. Higher speed is gained either by external power (engines), or by converting altitude to speed. More speed means that more altitude is converted to speed == higher descent rate.

@Masse if you're descending at a higher descent rate per minute, at a lower airspeed, you absolutely will lose more altitude per distance - anything else would be impossible. But again, you're discussing aerodynamics, which can vary more significantly, while I'm discussing airliner operation within a fairly defined set of activities. In short, you're over-complicating things

@Jon Story No, I think these are flight mechanics and you are wrong, by no means slower means more altitude per distance. That's why SIDs (at least those I am aware of) with climb restrictions express it in grade % and not in feet per minute.

@SteliosAdamantidis that's climb, not descent. And I've already clarified that this only applies to Airliners at speeds you would expect an Airliner to be descending at: which is almost without question below their best glide speed, therefore slower = higher descent rate. I include a caveat in the answer to explain that is not always the case, but that it is for the situations described

Guys, if you think I'm wrong please feel free to write your own, better answer and let the voting system sort it out... this is just becoming a convoluted chat in the comments section now and isn't really helping anything or anyone. An airliner descending at idle power at 150 knots will, for every single modern airliner of Q400 size or larger, descend at a higher rate than one at 200 knots, and that's the final input I'll be putting into this part of the discussion. If you disagree, please write a better answer.

If thinking through aerodynamics (all planes are affected by it), @JonStory answer is wrong, you get greater vertical speed with higher IAS. This is how gliders manage their speed, by converting altitude to speed (conversely speed to altitude). You want to go faster, push the stick, slower and you pull the stick. Altitude per distance is another matter which takes best glide into consideration, but altitude per time is directly related to speed. The only way to have slower descent and higher speed is by giving the aircraft more power, which can be considered 'airline operations'.

@masse again you are talking about an entirely different thing. We're discussing descent on autopilot/autothrottle, which in an airliner typically means idle power for most of the descent. If you need a higher rate of descent than is possible on idle power, you deploy spoilers. That's literally the point of this question. Please, people, unless you have an understanding of the properties of an airliner in descent (in which case I'd be delighted to discuss further or be corrected), can we take this to chat or write your own answer. You're just making the comments section confusing and messy

@JonStory in that case could I recommend that you modify your answer to accomodate some of this discussion? Clearly there are parts in your answer that doesn't please other aviators. Most likely we just misunderstood your answer or you omitted some parts.

@masse If I do that, I'll be taking the discussion out of scope of the question. I may look at the wording later if I have time, to see if we can avoid some of the confusion though


text:
What is the power source of the clock in glass cockpits?
I always get the impression that, once the shutdown & secure checklist is completed, there would be absolutely no electricity to any components in the cockpit or any aircraft systems.
However, most flight management computers know the current time. The time is also needed for GPS positioning.
How does the aircraft keep the time when the power is off? Is there a very small battery (similar to computer motherboards) which needs to be replaced once every few years, or is there a tiny electric current drawn from the batteries at all times?

GPS is actually a very accurate time source, rather than needing time to work.

You do NOT want to carry a clock in your aircraft that is accurate enough to "make GPS work" -- an atomic clock that accurate would be crazy expensive and probably pretty heavy & bulky as well.  The GPS receiver compares the signals it's getting from the satellites down to about a nanosecond, determines position, and gets time-of-day out of that as a byproduct.  The GPS receiver determines the time with FAR greater accuracy than any aircraft clock ever will.

Time is just yet another dimension (coordinate). If you can get your accurate position in 3D-space from a couple of satellites, then you can get your accurate position in 4D-spacetime the exact same way with just one extra satellite.

@JörgWMittag 1 sat = time, 2 sats = position in some circle of intersection (not generally useful), 3 sats = 2d position, 4 sats = position plus altitude

@GdD, while this is true, a real time clock (and a memory of the last position) greatly help with initial fix acquisition. There is an answer below that elaborates on that.

From Airbus FCOM

The clock has two electrical supplies, one of which is a direct connection to the aircraft battery hot bus

I cannot remember what the other supply was, but DC1 would be a good bet.
This seems to imply two things:
a) clock is powered by normal power distribution when generators are working (DC1)  and directly linked to main a/c battery when powered down (HOT BUS 1)
b) at least on Airbus the clock itself does not have its own tiny battery

There are two ways this generally works:

A low-current hot buss that is always connected to the system battery
A small rechargeable battery that powers low-power time and memory circuits

The first is common in aircraft with hard-wired systems, while the second is the case for nearly every handheld-style GPS.

While GPS does not necessarily need to be powered all the time, it dramatically speeds up the satellite position lock if it is

close to the correct time and
can produce the GPS 'almanac' (coarse orbit) from memory
can produce valid ephemeris (detailed orbit) data from memory
has a valid last known position

The time, position, and almanac information give the GPS hints on which satellites to search for first. Once the first satellite is locked on to it can acquire a time signal and the time is quite accurately synchronized to the GPS system. The almanac is successively used to search for more satellites that should be in view, but will fail over to look for others if these are not found. Once a satellite is found, if the ephemeris data has expired, it will listen for the ephemeris information which takes around 30 seconds to receive. This is the main difference in the 'hot' 'warm' and 'cold' start time for a GPS receiver.
If no power is maintained in the GPS, at the very least the time will be lost, and more typically all of the almanac information is wiped out as well, resulting in a position acquisition time of a minute or more.

Very interesting. It would be great if you could include some references. I'm not doubting you, but I'm sure someone, somewhere would like to read more on that.

As far as the aircraft wiring goes, it's just what I've seen. GPS receivers is the same. The rest of this is an extremely boiled-down description of the GPS lock acquisition process. Here is a description of the TTFF which pretty much says the same thing about cold warm and hot states: https://en.wikipedia.org/wiki/Time_to_first_fix

That's why mobile phones usually use aGPS (assisted / accelerated GPS), by getting 1) current time, 2) the almanac, 3) the ephemeris data, and 4) a rough guesstimate of the current position from the cell carrier network, at far greater data rates than from the GPS satellites themselves. The cell network provider may also provide dGPS correction data via the cellular network, improving accuracy.

Interestingly enough, large aircraft are not actually powered down as often as you would think. Much like your desktop computer there is most likely a small power source (often a small battery) that runs the clock(s) after it has been powered down (main shut down or main breaker shut off) (im looking for some exact references for this as well). There are lots of different avionics systems and combinations of equipment out there so the answer will of course vary from plane to plane as well.
On a bit of a side not the current time is not needed to figure out your GPS position although time is the coordinating element that the GPS network uses its more about the difference in time received from the satellites than your apparent local time.
The Piper Archer I fly simply has the clock wired to the main bus before the main bus switch so it can continue to run when the main switch is off.

Nice link to the B787 power up time issue.

I would say airliners are not actually powered down very often.  From my experience with large GA aircraft like jets, the operators will often power them completely down when stored in the hangar.


text:
How does contrail formation differ from turbofan to turbojet?
Air forces and intelligence agencies are indeed interested in predicting whether condensation trails (contrails) will be visible or not during aircraft operations.

Photo: C-CYOW at Photobucket
Among existing prediction algorithms, Appleman's method, devised in 1953, is frequently cited, even if more accurate or refined algorithms exist, like JETRAX.
From Predicting Contrails Using an Appleman Chart (Nasa), the principle is based on air saturation characteristics:

At first, scientists were not sure how contrails formed. We now know
  that they are a type of mixing cloud, similar to the cloud that
  sometimes forms from your breath during a cold winter day.
Appleman showed that when the air outside of the airplane is cold
  enough and moist enough, the mixture of the jet exhaust and the air
  would form a cloud.

Appleman chart, with a different layout
Since 1953, civil turbofans have replaced turbojets, with various air bypass ratios. What is the effect of this replacement on the occurrence of contrails?

Does turbofan reduce or increase contrail occurrence?
Does bypass ratio play a role?

It might be interesting adding piston-powered airplanes into the mix too since they did leave quite a bit of contrails in WWII.

It appears that the higher bypass engines available today increase the contrail occurrence. From Influence of propulsion efficiency on contrail formation by Ulrich Schumann:

The  thermodynamic  analysis,  which  is  the  result  of first-principle  arguments,  implies  that  aircraft  and  engines, performing with a higher overall propulsion efficiency release a smaller fraction of the combustion heat during cruise  into  the  exhaust  plume, and  hence  cause plume conditions which during mixing reach higher relative  humidity  for  the  same  ambient  temperature  and hence form contrails also at higher ambient temperatures.
Hence aircraft will form contrails more frequently when
using more fuel efficient engines.

TO test the theory, a flight test was conducted between two aircraft with low and high bypass engines:

For a direct test of the theory, a formation flight of two different large  jet aircraft was arranged, wing by wing, during an ascent and a descent f the aircraft. Contrail formation and ambient conditions were observed simultaneously from a research aircraft.
The two contrail forming aircraft were
(i) a Boeing B707 equipped with four jet engines of type JT3D-3B with bypass-ratio of 1.4 and
(ii)  an  Airbus  A340-300 with  four  jet  engines  of  type
CFM56-5C4  with  bypass-ratio  of  6.8.

The results indicated that contrails were formed in more instances in case of the A340 (with higher bypass engines) compared to the B707.

Photo of an A340 with contrail and B707 without one. Image from Influence of propulsion efficiency on contrail formation by Ulrich Schumann

Ambient  conditions were measured and the contrail formation was observed from a research aircraft flying less than 1 km behind the two contrail forming aircraft. As documented in several photos, an altitude range exists in which the A340 causes  contrails while  the  B707  causes  none.

Though the sample size is pretty small, it does appear that the high bypass engines used in modern commercial aircraft are more prone to contrail formation compared to the older turbojets.

@mins Contrails are formed when the warm, unsaturated engine exhaust mixes with the cold ambient air. The important thing here is the ratio of moisture to heat added to the wake. This is the critical factor,that decides when contrail is formed.


text:
Is the Brodie landing system still in use somewhere?
The Brodie system was a method for taking off and landing without a runway, circa 1945. The landing or taking off aircraft was hung on a wire held at the appropriate height:

From PhotoBucket, Duggy009
It could be used on a ship too:

From Youtube: Brodie Landing System
Two advantages of this system: Easy to conceal and capacity to operate to/from areas unsuitable for an airstrip.
This system seemed promising, especially for armies, but I never heard of subsequent use. Why was it discarded? or if it wasn't, what application do/did exist following this WW2 experimentation?.

Much like carrier landing, such landings would be another major set of stresses on the airframe. So, it requires extra structural strength and hardpoints, adding weight and reducing the effectiveness of the plane.  With the proliferation of helicopters, aircraft carriers, and aerial refueling, the need for this kind of system all but evaporated.

I'm not aware of the Brodie landing system used anywhere now. The system was actually a response to the pressing problem of non-availability of escort carriers in required numbers, similar to the British CAM ships, that launched hurricanes on one-way missions. The only difference being that the aircraft could be retrieved here.
The main advantage of the system is its ability to operate from (cargo) ships and LSTs, which became less important as the war progressed and more and more aircraft and escort carriers became available. There were some disadvantages too- it required certain skill from the pilot for landing (especially if installed in a jungle or on the top of a building). Also, a 600' cable between two 65' posts can hardly be called small (and as @ymb1 noted, it is hardly practicable for larger aircraft).
Helicopters serve the same purposes- operate from anywhere with much heavier payloads and in non-existent airstrips routinely.
However, similar systems are used for retrieval of small UAVs. For example, the Boeing Insitu ScanEagle uses a similar system of retrieval (though the launching system is different). From uavglobal.com:

ScanEagle needs no airfield for deployment. Instead, it is launched using a pneumatic launcher, patented by Insitu, known as the “SuperWedge” launcher. It is recovered using the “Skyhook” retrieval system, which uses a hook on the end of the wingtip to catch a rope hanging from a 30-to-50-foot (9.1 to 15 m) pole.

Scan Eagle retieval; By United States Navy, Mass Communication Specialist 3rd Class Kenneth R. Hendrix - Navy NewsStand Photo ID: 071114-N-5758H-065Navy NewsStand Home, Public Domain, Link

There are patents for a number of similar systems (eg 1,2 and 3). Interestingly, Insitu calls its skyhook system:

... the first capture system to eliminate runways and nets

Apparently, they didn't get the memo.

Besides, if you need to operate a tactical aircraft out of something other than a conventional runway or CATOBAR/STOBAR carrier, that's what Harriers are for ;)

My Uncle worked on installing this system in India, Digri in July 1945. First problem was the tensioning of the wires which caused the pylons to buckle. So they found a new location and this time the wire anchors to the pylons pulled out of the ground due to ground conditions. In the end it was deemed a failure, was packed up, loaded on a train and never heard of again. I do remember him showing and instruction book on the system may years ago. He's passed on so whether is wife has that I don't know.